Abstract

The Don Valley Brickyard in Toronto is an internationally designated type site in recognition of diverse faunal remains in the Don Beds of last (Sangamonian) interglacial age; pollen in overlying strata record the climatic deterioration marking the onset of the last (Wisconsinan) glacial cycle. New sedimentological descriptions show that the Don Beds, about 8 m thick, were deposited in a lacustrine lower shoreface environment subject to episodic storms. Storm-deposited sand facies are interbedded with peaty muds that are extensively bioturbated. Water depths, derived from wave-formed ripples using linear wave theory, appear to have increased during deposition of the Don Beds from about 2 m to about 18 m (12–28 m above the modern lake level), a change that is recorded by an overall fining-up sequence. Increasing water depths may have been the result of isostatic recovery of the lake outlet to the east. The Don Beds overlie a thin bouldery deposit, possibly a remnant of older Illinoian glacial sediments (York Till). The interglacial beds pass up into prodelta rhythmites (Scarborough Clays) of a regionally extensive delta body, indicating continued deepening. Deepening was accompanied by steadily decreasing mean annual temperatures; upper deltaic sediments (Scarborough Sands), exposed to the east along lakeshore bluffs, were deposited in a cold-climate setting during the opening phase of the Wisconsin glaciation.

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